In prior art the standard brass is an alloy comprising at least copper and zinc. However, different added alloying elements may provide an alloy that can advantageously be used to manufacture items for special use. For example, the seven most used commercially available brass alloys are as follows:                CuZn15 Red brass        CuZn30 Cartridge brass        CuZn30Sn1 Admiralty brass        CuZn40 Muntz metal        CuZn40Sn1 Naval brass        CuZn40Pb1Sn1Fe1Mn0.3 Manganese bronze        CuZn22Al2As0.05 Aluminium brass        
As readily understood, these brass alloys have different material properties that are beneficial when producing for example ammunition, using the alloy in marine environments etc.
Generally, the ability of the brass alloy to be subject to machining is an important parameter which reflects how the brass alloy provides wear and tear of tools that are used during the machining process. Wear of tools are an important economical parameter in production plants. Some of the interesting parameters during production comprising using brass alloys are:                state of surface of the machined parts        cutting speed        fragmentation of chips        lifetime of the tool        
Also, the ability for casting the brass alloy is important, for example 10 temperature level for casting, cooling time providing restructuring of the alloy etc. Further, it is also important how easily a brass bolt for example may be extruded. For example, resistance towards cracking when extruded, the force that is necessary to apply when extruding, time that must be used for achieving an end result etc. All of these parameters are possible to control, to alter, to enhance etc. with addition of different alloying elements when manufacturing the brass alloy. For example, addition of lead may improve the ability for machining the brass alloy as known to a person skilled in the art. The content of Zinc in an alloy is primarily an economical way of producing a cheaper alloy (reduces the content of copper). One problem with the Zinc is the process of dezincification when the brass alloy is in contact with water. This is for example the case with brass components used in water supply systems. It is known in prior art that for example arsenic added in small portions as an alloying element stops or reduces significantly dezincification of items made of brass alloy in water.
The phase map of a copper-zinc system (ref. FIG. 1) illustrates that in the range of 0-40% Zn in the brass alloy, the brass can be structured in two different phases, α and β, depending on the temperature and the composition of the alloy. Below 35% Zinc, alloys are exclusively α phase. But between 35% and 40% Zinc, the structure can be either a pure α phase or a mix of α and β phase, which is called duplex structure. The β phase is preserved at room temperature but is subject to a long range ordering at 454° C. to form β′. This ordering reaction cannot be avoided even by drastic quenching. FIG. 2 illustrates some of the structures. At room temperature, the α phase has a minimum when there is 64% Cu content in the alloy, while the β′ phase has a maximum when there is 54% Cu content in the alloy. The structure of the alloy determines very important properties of the alloy as known to a person skilled in the art. The two most important parameters are the resistance towards corrosion and the ability to be cold or hot deformed.
The ability of the brass to be shaped is dependent upon the temperature and the structure of the alloy. It is known in prior art that α phase provides a brass with very good ability to be cold worked while the brass withstands hot working.
Contrary, the β phase has a very low resistance towards hot working. The duplex brass is known to be the most easily worked copper alloy because it combines the advantages of both α and β phases. Thus it has respectively both hot and cold working abilities.
With reference to the phase map in FIG. 1, the α phase comprises more copper than the β phase. The α phase is therefore more noble than the β phase. It means that when the two phases are present (duplex brass), a galvanic connection is formed and the β phase, which is the less noble one, will be corroded first.
Thus, a duplex brass cannot in any case be protected against corrosion, due to its nature of a mix of two phases.
A pure α structure can be protected against corrosion if an inhibitor is alloyed in small amounts.
Arsenic, phosphorus and antimony are known examples providing protection against dezincification. However, there is a risk of inter granular corrosion. Therefore, the content of such alloying elements are usually very small.
However, it has been known for some time that for example lead pollution from brass alloys (used to enhance machining ability) is harmful to the human body. [W. Heller, Copper based alloys in Materials Science and Technology, Eds. R. W. Cahn, P. Haasen and E. J. Kramer, Vol 8, Chapt. 6 (1996)].
Recent epidemiological research finds that even exposure to low-level concentrations of lead over long periods of time can badly affect the development of infant intelligence and it is said there is some effect on hormonal development [Kentaro Iijima, Takamitsu Otake, Jun Yoshinaga, Miyuki Ikegami, Emiko Suzuki, Hiroshi Naruse, Tomoya Yamanaka, Noriko Shibuya, Takehiko Yasumizu and Nobumasa Kato, Biological Trace Element Research, Cadmium, Lead, and Selenium in Cord Blood and Thyroid Hormone Status of Newborns, Volume 119, Number 1/October, 2007, pp. 10-18]. As a result government agencies and private industry are making efforts to reduce lead content in products used in distribution of drinking water. [California, Czech].
Typical copper alloys used in the production of brass rod, brass forging and bronze casting contain several percentage points of lead to improve ability of machining the alloy [H. Sigurdsson, Dezincification and stress corrosion cracking of brass—A literature survey, Raufoss Materials Technology report Jul. 10, 1999, (1999)].
Unfortunately lead content results in environmental problems such as lead leaching into the drinking water, lead dust during machining and casting, and disposal of lead-contaminated foundry sand. Hence it has long been desired to develop lead-free brass alloys that do not harm humans or the environment. In addition, maximum content of other heavy metals like arsenic is debated.
Further, Arsenic, Phosphorous and Antimony leaking from brass alloys to the surrounding environment may be a hazard due to possible toxic properties of such alloying elements.
In prior art CN 1616695 describes a brass alloy comprising 80-84 wt % Cu, 2.5-5 wt % Si, 0.02-0.1 wt % As and the rest is Zinc.
20 JP 56009347 disclose a brass alloy comprising 25-37 wt % ZN, 0.005-2 wt % Si, 0.002-0.5 P, the rest is Cu.
JP 58022347 disclose a brass alloy comprising 25-35 wt % Zn, 0.005-2 wt % Si, 0.005-0.5 wt % P and the rest is CU.
GB 1443090 A discloses brass alloys comprising copper, zinc and silicon with addition of an inhibitor like arsenic. In Table II in the publication the dezincification resistance performance of different alloys are presented. All alloys providing dezincification resistance comprises arsenic levels from 0.03 wt % and upwards. It is also disclosed that an alloy with 79 wt % copper and 3-4 wt % silicon can achieve dezincification if the arsenic level is 0.01 wt %. In general has all the disclosed alloys in this publication has a copper level of 74 wt % copper and upwards. This implies that the microstructures of the alloys will be either a pure α phase or a mixture of α- and ζ-phase.
FR 2356733 A1 discloses alloys comprising copper, zinc, silicon, manganese, arsenic, aluminum and tin. Lead is added to achieve machining capabilities. These alloys exhibit possible hazards to the environment as described above.
Hence, an improved brass alloy would be advantageous, and in particular a more environmental friendly brass alloy that at the same time provides good material properties for different manufacturing processes comprising the improved brass alloy, and at the same time may be produced according to an economical and technical efficient method for production of the brass alloy according to the present invention.